A "tsunami" of match-fixing is plaguing lower-level tennis events, according to an investigator in a long-awaited report into corruption in the sport.
But the Independent Review Panel (IRP) found no evidence of a cover-up of these issues by governing bodies or the Tennis Integrity Unit (TIU).
The report also shows no evidence of top-level players being implicated.
The two-year review - which BBC Sport understands cost close to £20m to fund - spoke to more than 100 players.
It also surveyed more than 3,200 professionals. Of those surveyed, 464 said they had first-hand knowledge of match-fixing.
Led by Adam Lewis QC, the panel was set up in January 2016 after a BBC and BuzzFeed News investigation uncovered suspected illegal betting.
It found a "very significant" corruption problem at "lower and middle levels of the sport" which Lewis described as a "fertile breeding ground for breaches of integrity".
He also said that from 2009 to 2017, men's matches were responsible for 83% of alerts to suspicious matches.
The report also shows "evidence of some issues" at higher levels, such as Grand Slams and Tour events, but the evidence does not reveal a "widespread problem" in elite professional tennis.
Asked if tennis fans could believe what they are seeing at major tournaments this summer, Lewis replied: "Yes, the data shows that there is very little incentive to breach integrity, therefore it's unlikely you are going to see match-fixing."
Other key findings and recommendations include:
- Report authors were told of a "match-fixing 'season'" from October until the end of the year with "traces of up to two or three fixed matches per day" in International Tennis Federation (ITF) tournaments
- investigations at Grand Slams were "insufficient", while the ATP, the organisational body of men's professional tennis, was guilty of "failing to exhaust potential leads before ending investigations"
- the sale of official live scoring data, at least at ITF and Pro Circuit levels, should be discontinued because it has increased the problem
- adopting a realistic approach to how many players can be considered professional.
- and a reorganisation and reform of the TIU, the sport's anti-corruption body.
The report also proposes an end to betting sponsorship in tennis, especially tournaments.
It draws on statements from more than 200 key stakeholders in professional tennis, including from governing bodies, tournament organisers and betting operators.
'A fertile breeding ground' - why match-fixing is taking place
In the course of its investigation, the panel was told by one betting operator that "the situation in tennis was grimmer than grim".
But report author Lewis maintained that suspicious matches were more suited to lower levels of tennis where a blend of factors came together to create "a fertile breeding ground".
Chief among them include the number of players struggling to make a living, few people watching the matches in person and the ITF's decision to sell official live scoring data in 2012, making betting on lower-ranked matches far easier to achieve.
"Only the top 250 females and 350 male players are making enough money to break even before coaching costs, yet there are 15,000 nominally professional players," Lewis said. "It's a small step for a player who already intends to lose for other reasons to then bet or inform others of his or her intentions so as to make enough money to continue playing."
He also said the number of alerts to suspicious matches had risen from three in 2012 - the year the ITF sold live scoring data - to 240 in 2016.
"According to [European Sports Betting Integrity firm] ESSA, since 2015 tennis has been responsible for more suspicious betting than for any other sport in each and every quarter," Lewis said.
The report added that since the data deal, 60,000 matches were available to the betting market in 2016, up from 40,000 in 2013.
As well as recommending that the sale of scoring data should discontinue "at least at ITF and Pro Circuit levels", the report also said tennis should stop tournaments being sponsored by betting firms and governing bodies should introduce measures to deal with the "intolerable levels of online abuse, often from disappointed bettors".
Is the TIU fit for purpose?
Although the TIU has been cleared of any cover-up of match-fixing, Lewis said its staff were made up of former law-enforcement offers and included no tennis or betting experts.
And while the number of staff had increased from six to 17, he said there were "too few staff to combat the problem".
The report also contained numerous examples of how the TIU - which is funded by the sport's major stakeholders - should reform, be more accountable and improve its independence, including a move away from its current home at Roehampton, the same west London site where the ITF resides.
Other reforms could include:
• A new board, independent from governing bodies.
• More, and more diverse, staff to deal with the scale of the problem, and be more transparent, including an annual external audit.
• Make better use of betting data and match footage to support disciplinary proceedings, improve its processes for gathering and storing intelligence.
• Make the disciplinary process more streamlined and cost-effective, and make greater use of criminal law.
Tennis bodies agree to recommendations
The governing bodies of professional tennis - the ATP, WTA, ITF and Grand Slam Board - released a joint statement in response to the report, agreeing with its findings and confirming an "agreement in principle" to implement all the recommendations.
They said they "recognise" the "vulnerabilities" in the sport, particularly at lower levels, and are "committed to seizing the opportunity to address these concerns through firm and decisive action".
The statement also welcomes the IRP's finding that the panel has "seen no evidence of any institutional corruption" or a cover-up by tennis authorities and the TIU.
But it does not directly address the report's judgement the ATP "failed to exhaust potential leads before ending investigations".
Each body will conduct "detailed exploration and analysis" before responding to the 12 recommendations prior to publication of the final report.
BBC tennis correspondent Russell Fuller
The panel found no evidence of a cover up, or corruption at the top level, but describes a system ill-equipped to deal with the substantial threat at lower levels.
The TIU, according to the report, is "overly conservative" and should make greater use of betting data to bring about convictions. Many defence lawyers may argue this type of evidence is purely circumstantial.
The panel says the problem of betting on lower level matches would be much reduced if the live scoring data sold by the ITF in 2012 in lucrative deal in was severely restricted. Sportradar, the data company with whom the ITF is in partnership, has already warned this appears unrealistic, potentially unlawful and will not prevent betting on these matches.
So there will be much debate before the final report is published, and the governing bodies carry out their promise to implement the findings in full.
There is also a call for national governments to introduce stricter criminal liability for sporting corruption, and a suggestion that appearance fees are capped and publicised in the interests of greater transparency. That will not go down well with those at the elite levels of the sport.